1. Field of the Invention
The present invention relates to a shock protection apparatus for a hard disk drive, and more particularly to a shock-cushioning apparatus for protecting a hard disk installed on a device from shocks as a result of the device being dropped.
2. Description of the Background Art
A hard disk drive (hereinafter referred to as a “HDD”) is a device that stores or reproduces data in a desired storage location by moving its magnetic head to the desired location in a head load state where a predetermined amount of clearance (flying height) is maintained between the head and the surface of a disk rotating at high speed. To increase the recording density of HDDs, the distance of the flying height between the disk surface and the head slider surface is getting smaller year by year.
During the operation of a HDD, if a violent impact force in the vertical direction is applied to the recording surface of a disk, in particular, there is a high possibility of causing a phenomenon known as a “head slap” where the head slider hits the disk surface due to the head slider being displaced by a distance greater than the flying height. The head slap may cause physical damage to the recording surface of the disk or to the head, whereby it becomes impossible to store/reproduce data located in at least a damaged part of the disk. In the worst case, the entire recording surface of the disk may become unusable, i.e., the HDD may get damaged.
In the case where a HDD is installed on a stationary device, represented by a desktop computer, a violent impact force which may cause a head slap is rarely applied to the HDD. On the other hand, in the case where a HDD is installed on a portable device, represented by a notebook personal computer (hereinafter referred to as a “notebook PC”), it is not an exaggeration to say that the HDD is often subjected to a violent impact force. Specifically, because of the portability of notebook PCs, etc., the user can easily carry or move the notebook PC, etc. During carriage or moving, the user may accidentally bump or drop the notebook PC against or onto a hard surface. Since notebook PCs, etc., are designed to be compact and light-weight so as to ensure portability, such an impact force may be easily transmitted to the HDD incorporated in the computer, thereby damaging the HDD.
To avoid such a problem, a recent, small HDD which may be incorporated in a notebook PC or the like, is equipped with a head retracting mechanism to improve shock resistance during operation, in particular. For example, in a 2.5-inch HDD, during non-operation or even during operation in an idle state where there is no access request for a predetermined period of time, the head is retracted at a location away from the disk by a head unload operation. In the head unload operation, the head actuator is moved into a comb-shaped retract component, known as a “ramp”, which is provided at a location away from the disk, and at this location the head actuator is locked by a magnetic latch structure provided at the lower part of the magnet yoke of a voice coil motor. In this manner, the aforementioned physical damage to the head or the disk surface caused by a violent impact force acting in the vertical direction on the recording surface of the disk can be avoided.
The aforementioned head retracting mechanism changes the shock resistance of the HDD by unloading the head in accordance with the change of the operation mode of the HDD. Specifically, when the HDD is in a mode where the HDD does not need to be located over the recording surface of the disk, the head is retracted from the disk, thereby preventing the occurrence of a head slap. On the other hand, during storage or reproduction, the head needs to be located over the recording surface of the disk, and thus the head is not retracted. Namely, shock protection of the HDD is realized by controlling the HDD such that the resistance of the HDD to an impact force of the same magnitude changes depending on the operation mode of the HDD.
Since the head is in a head load state not only during an access operation to the disk (i.e., the HDD is in an operating state) but also immediately after the access operation (i.e., the HDD is in a non-operating state), the occurrence of a violent impact force in the vertical direction being applied to the HDD immediately after the access operation, may produce a head slap, thereby damaging the head or the disk. That is, when the HDD is in a head unload state and at the time of changing its operation mode, the HDD cannot appropriately handle abrupt, violent impact forces.
FIG. 5 illustrates an exemplary shock-cushioning structure mounted to a HDD and having a shock-cushioning function which acts consistently regardless of whether the HDD is at the time of changing its operation mode, so as to protect the HDD from violent impact forces at all times. A shock-cushioning structure SU encloses apart or all of a HDD 1 with a shock-cushioning material, such as special elastic rubber or urethane sponge, so as to cushion shocks applied to the HDD 1. A shock-cushioning material 52 is used in the shock-cushioning structure SU to extend the duration of a shock, which is the length of time an impact force, caused as a result of the note PC dropped and crashed onto the ground or the like, is transmitted to the HDD 1 installed on the note PC, thereby reducing the peak value of a shock acceleration wave. The protection structure of the HDD 1 using a shock-cushioning material has been employed not only in notebook PCs but also in devices such as a compact, light-weighted MP3 recording/playing device having the HDD 1 installed thereon.
The shock-cushioning characteristics of such a shock-cushioning structure may be determined by the shock-resistant performance of a HDD 1 to be protected. The device specifications which indicate the shock-resistant performance of the HDD 1 specify shock resistance values for two states; an operating and non-operating states. Exemplary shock resistance specifications of a 2.5-inch HDD are as follows: The shock resistance specification (X/Y/Z directions) during operation is 200 G (the duration of action is 2 msec) and the shock resistance specification (X/Y/Z directions) during non-operation is 800 G (the duration of action is 1 msec).
The X/Y/Z directions indicate two directions (X/Y) which define the recording surface of a disk and a direction (Z) perpendicular to the recording surface of the disk. The impact force to be transmitted to the disk has a half-sine wave shock wave. The HDD 1 satisfying the above specifications can withstand a half-sine impact force of 800 G (gravity) acting in the X, Y, Z directions for a period of 1 msec during non-operation, and can withstand a half-sine impact force of 200 G for a period of 2 msec during operation.
Namely, in order to protect the HDD 1 from shocks, a shock-cushioning structure SU requires the function of cushioning impact forces so that an impact force of 200 G or greater cannot be applied to the HDD 1 during the operation of the HDD 1 and that an impact force of 800 G or greater cannot be applied to the HDD 1 during the non-operation. This will be described below by taking an example where a cushioning structure is used in which when the notebook PC is dropped from a height of 90 cm, an impact force of only 500 G at a maximum is applied to the HDD 1. That is, since the shock resistance specification during the non-operation is 800 G, the HDD 1 can withstand an impact force of 500 G with an allowance of another 300 G during the non-operation.
However, since the shock resistance specification during the operation is 200 G, the shock resistance falls short by as much as 300 G, with respect to an impact force of 500 G. Therefore, if an impact force of 500 G is applied to the HDD 1 during the operation, i.e., in a head load state, physical damage may occur due to a head slap phenomenon. That is, with this cushioning structure, the HDD 1 installed on the notebook PC cannot be protected from shocks resulting from drops of 90 cm, during the operation.
As shown in FIG. 4, in order that the HDD 1 can withstand drops of 90 cm during the operation, the amount of a cushioning material needs to be increased to lessen the shock to 200 G or lower, or the elastic modulus needs to be increased. However, it is very difficult to design a shock-cushioning structure which satisfies both operating and non-operating conditions.
On the other hand, the type of shock wave generated when the notebook PC incorporating the HDD 1 free falls can be a pulse wave with a short duration of action or can be a repeating pulse wave with a long period, rather than the a half-sine wave specified by the device specifications. The diversity of shock waves results from the material or rigidity of the cabinet (casing) of a notebook PC and/or the mounting structure of the HDD 1. With an increase in complexity of the shock wave to be actually generated, it is important to perform a series of product drop tests by actually dropping a device having the HDD 1 installed thereon, so as to select an appropriate mounting structure and shock-cushioning material based on the test results.
Further, in order to obtain a desired cushioning effect, a shock-cushioning material is compressed in advance by a predetermined pressure. This advance compression generates concerns about the deterioration of elasticity of the shock-cushioning material resulting from change over time. In addition, the change over time causes a decrease in the volume of the shock-cushioning material. That is, as a result the deterioration of elasticity and a decrease in volume, the shock-cushioning material would lose its originally-set desired cushioning effect.
In order to maintain a desired cushioning effect, it is necessary that the amount of change over time, which may cause elasticity deterioration, a volume decrease, a reduction in a cushioning effect, or the like, be estimated in advance so as to produce a shock-cushioning structure using an extra amount of a shock-cushioning material which corresponds to the estimated amount of change over time. However, the use of extra amount of a shock-cushioning material to compensate the change over time may become a great impediment to designing a compact, light-weighted notebook PC whose portability is very important.
As described above, problems in techniques for improving the shock-resistant performance of a HDD using a shock-cushioning material can generally be divided into the following two groups. The first problem is the necessity of estimating in advance a reduction in cushioning performance of a shock-cushioning material resulting from the change over time and adding a sufficient volume of the shock-cushioning material to compensate the estimated reduction in cushioning performance. To do so, the device having the HDD installed thereon needs a space therein for enclosing the added cushioning material, which hinders obtaining a compact and light-weighted device.
The second problem is that materials capable of providing a shock-cushioning effect which satisfies required specification values for both operating and non-operating conditions do not exist or are not yet in actual use, and thus are not available. This necessitates the use of a plurality of materials with different elastic moduli which are separately designed for operating and non-operating states, making the structure of a shock-cushioning structure complicated.
Further, a technique is suggested in which an acceleration sensor is used to avoid the occurrence of a head slap during the operation (i.e., during or immediately after an access of the head to the disk) in the aforementioned head retracting mechanism. In this technique, the acceleration sensor is incorporated in the HDD, and when the acceleration sensor senses a predetermined acceleration, the head is urgently retracted for unloading, regardless of the operation mode of the HDD. That is, in a conventional head retracting mechanism, the head is unloaded based on what is called an operation mode, i.e., based on the access condition of the head of the HDD to the disk recording surface, whereas in the aforementioned technique the movement of the HDD is perceived as acceleration and the magnitude of the perceived acceleration is perceived as the sign of a head slap to retract the head, thereby reducing the probability of delay in retracting timing of the head.
However, in practice, the acceleration applied to the HDD during free fall changes from 1 G to 0 G. Thus, it is nearly impossible for the acceleration sensor to detect such a small rate of change in acceleration. In order to amplify the rate of change in acceleration detected by the acceleration sensor, a signal processing circuit such as an amplifier circuit is required. In addition, regardless of whether the rate of change in acceleration is amplified or not, because the rate of change in acceleration to be detected is basically small, the threshold to determine whether the HDD is dropping or not needs to be set to a low value. However, if the threshold for determination is too low, even vibrations generated by the HDD itself or transmitted externally may also be falsely detected as a drop of the HDD. To prevent such a false detection, a special signal processing technique is required.
The head retracting mechanism which operates based on the operation mode of the HDD, the head retracting mechanism which operates based on the change in acceleration of the HDD, and the shock-cushioning structure using a shock-cushioning material, as discussed above, have problems protecting the HDD installed on a portable device, such as a notebook PC or information terminal, from shocks. To obtain a shock protection apparatus which can complement the aforementioned individual specific problems, it is desirable to combine a shock-cushioning structure and an emergency retracting mechanism for the head which operates based on detections of head-slap signs by means of an acceleration sensor.
Even with this combination, shock-cushioning materials which can absorb, by themselves, the difference of as much as 600 G between operating and non-operating states have not been yet found. Further, it is very difficult to construct a shock-cushioning structure using a plurality of shock-cushioning materials, which can absorb the difference of 600 G. Even if it is constructed, such a shock-cushioning structure is complicated and large in size and weight, and thus cannot be used in a portable device whose being compact and light-weight are important, as is the HDD to be protected. In addition, a problem resulting from degradation of the shock-cushioning properties of a shock-cushioning material due to the change over time cannot be solved. Further, it is obviously impossible to solve a problem resulting from the fact that the acceleration sensor cannot promptly and properly detect a head-slap sign of the HDD.